This year's release of Firefox 3.5 gave us a lot of reasons to like it, but its extensibility remains everyone's favorite feature. These add-ons and theme tools were the most popular in the year gone by.

Windows/Mac/Linux: The final version of the Firefox is starting to show up on Mozilla's web…
Read more Read more

This list is culled from a straight listing of the most popular posts that offered a Firefox extension for download in 2009. We're not including posts about configuring Firefox, or even our own hand-rolled Firefox add-on packs—even if they were pretty popular, too. Let's get to the good stuff.

Google Redesigned, a multi-site suite that trades Google's blue/white/minimal look for a darker, sleeker feel, kept improving its transformative powers this year, adding a host of improvements in its 3.0 release, and later releasing a new version with GReader Redesigned for the RSS hounds.

Many of the pictures and illustrations you find across the web aren't in their original form—and many can be had at better, perhaps more wallpaper-worthy sizes. The TinEye extension makes it a simple right-click maneuver to search out similar copies of any image you come across.

Sometimes, great stuff has to be hosted on public download services, because the file—or the attention it's getting—is just too much for our meek little personal sites. And the download sites often make it as painful as possible to grab those files. SkipScreen acts as an automated intermediary, jumping through the necessary hoops and entering the key presses required.

This neat little extension, winner of the Extend Firefox 3.5 contest, utilizes lots of Firefox's built-in features, like geo-location and the extension framework, to offer wary laptop users a way to nuke their personal data, passwords, and history if necessary, track where their machine is logging on after a theft, and cull all kinds of data from the thief. FireFound is, in other words, a smart thing to install if your laptop ever leaves the home.

A lot of helpful stuff is tucked away in Firefox's about:config menus. Gui:config brings them into focus and offers a graphical way to manage them. As the How-To Geek puts it, it's amazing that this isn't something being considered for mainstream distribution in the browser.

(Windows only): Firefox is decently light with memory on startup, but extensions and plug-ins drag it down as you actually use it. Memory Fox monitors Firefox's memory use and, once it reaches your pre-set limit, whips it back into shape.

(Windows only): Well, the headline and picture kind of say it all about Daum Blue, but it's worth noting that beyond looks, it's also fairly customizable, and looks even better on Vista and Windows 7 systems.

If you're likely to do more at a web site than just simply bookmark it, UrlbarExt is like a Leatherman for your AwesomeBar. Head to a site's root, search the site on Google, and do much more from a small array of address bar buttons.

Another headline that pretty much says it all. We weren't a big fan of Xmarks' new "discovery" features, but its growing reach into Chrome and other browsers make the former Foxmarks' expansion a good thing.

Given the recent legal crackdown on BitTorrent-centered sites, magnet links (explained here) are increasingly popular. Magnetiser makes it easy to track down a working torrent link to grab the file you're looking for.

It must be mentioned that, beyond smooshing together Gmail, Google Calendar, and Google Reader into one neatly-arranged Gmail page, Integrated Gmail also customizes every niggling detail of those combined apps, making it worth the try-out, even if you think you like your Google spaces separated into different tabs.

If you're always looking at online purchases and wondering if you could save more before pulling the trigger, Invisible Hand affirms your hunches for you, dropping down and showing lower prices wherever it can find them.